A mobile terminal device is required to be smaller and lighter from the viewpoint of improving portability. However, when considering operability, there is a limit to the reduction in the size of operation keys. In addition, there is a demand for the screen size of a display screen to be large. For the coexistence of such contrary requests, in the latest mobile terminal devices, generally, a display case provided with a display screen is connected to an operation case provided with operation keys by a hinge, and a display panel including the display screen of the display case is opposed to an operation panel including the operation keys of the operation case, thereby being foldable (generally, referred to as a close state: a folder close state).
In addition, a mobile terminal device was proposed in which an operation case and a display case can be relatively turned about a second turning axis, using a 2-axis hinge having a first turning axis for folding and the second turning axis perpendicular to the first turning axis. In such a foldable mobile terminal device, it is possible to view a display screen with the whole mobile terminal device in a compact state, by folding the display panel outward and folding the operation panel inward (referred to as a turn-close state).
However, in the state of folding the display panel outward, that is, in the turn-close state, the operation panel is on the inside, and thus there is a problem that the operation keys cannot be operated. In the past, a mobile terminal device was proposed in which operation keys (cross key) are provided on a display panel, and thus it is possible to input a key operation even in the state (turn-close) of the display panel being folding outward (e.g., see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open No. 2006-020273